We are investigating the binding of small ligands to heme proteins with flash photolysis in the time range from a few ns to a few ks, the temperature range from 4 to 300 K, and the pressure rang from 0.1 to 200 MPa. Binding involves three main steps, the solvent-protein interface, protein barriers, and a barrier at the heme. All three main steps are being explored for different ligands and different proteins. At the lowest temperatures, below about 30 K, binding occurs from the vicinity of the heme iron and proceeds via quantum-mechanical molecular tunneling. The parameters describing tunneling are being determined. At temperatures above about 200 K, the biomolecules do not remain in one state but rapidly change from one state to another. Properties of this conformational relaxation are being studied. A theoretical description of binding and conformational motion based on stochastic equations is developed.